Switchable glass or switchable windows in its application to windows or skylights refer to glass or glazing that changes light transmission properties when voltage, light or heat is applied.
The aforesaid glasses or windows control an amount of light (and thereby heat) transmission. When activated, the glass changes from transparent to non-transparent and blocks some or all wavelengths of light. Different mechanisms such as electro-chromic, photochromic, thermo-chromic, suspended particle, micro-blind and liquid crystal can be used.
Specifically, in polymer dispersed liquid crystal devices (PDLCs), liquid crystals are dissolved or dispersed into a liquid polymer followed by solidification or curing of the polymer. During the change of the polymer from a liquid to solid, the liquid crystals become incompatible with the solid polymer and form droplets throughout the solid polymer. The curing conditions affect the size of the droplets that in turn affect the final operating properties of the “smart window”. Typically, the liquid mix of polymer and liquid crystals is placed between two layers of glass or plastic having a thin layer of a transparent, conductive material followed by curing of the polymer, thereby forming the basic sandwich structure of the smart window. This structure is in effect a capacitor.
Electrodes from a power supply are attached to the transparent electrodes. With no applied voltage, the liquid crystals are randomly arranged in the droplets, resulting in scattering of light as it passes through the smart window assembly. This results in non-transparent appearance.
When a voltage is applied to the electrodes, the electric field formed between the two transparent electrodes on the glass causes the liquid crystals to align, allowing light to pass through the droplets with very little scattering and resulting in a transparent state. The degree of transparency can be controlled by the applied voltage. This is possible because at lower voltages, only a few of the liquid crystals align completely in the electric field, so only a small portion of the light passes through while most of the light is scattered. As the voltage is increased, fewer liquid crystals remain out of alignment, resulting in less light being scattered. It is also possible to control the amount of light and heat passing through, when tints and special inner layers are used. It is also possible to create fire-rated and anti X-Ray versions for use in special applications. Most of the devices offered today operate in on or off states only, even though the technology to provide for variable levels of transparency is easily applied. This technology has been used in interior and exterior settings for privacy control (for example conference rooms, intensive-care areas, bathroom/shower doors) and as a temporary projection screen. It is commercially available in rolls as adhesive backed Smart film that can be applied to existing windows and trimmed to size in the field.
Conventional practice in quality assessment of the switchable PDLC glass is in inspection of electrical, optical and mechanical properties of end products which are rejected because of electric or optical defects of PDLC film laminated between the two glass plates. Defect correction after lamination is impossible. There is a long-felt and unmet need to provide a method of step-by-step operation checking switchable PDLC glasses directed to reduction of rejection rate.